The present invention relates to a polarization dependent loss measuring apparatus, and particularly to a polarization dependent loss measuring apparatus for measuring loss dependent on a polarized wave of a measured object such as an optical element or an optical transmission line.
A polarization scanning method is known as a measuring method of polarization dependent loss (hereinafter called PDL). The polarization scanning method is a method in which while changing a polarization state of light incident on a measured object every one wavelength by a polarization controller, transmitted light from the measured object is measured by a power meter and a difference (dB scale) between the maximum loss value and the minimum loss value of measured values within certain time is measured as the PDL.
In order to measure the PDL of the measured object exactly, it is necessary to measure all the polarization states. On the other hand, in order to generate states equivalent to all the polarization states by the polarization controller, it is necessary to generate polarization states of the order of 500 randomly. Because of this, measurement time per one wavelength becomes 500 times that of the case of making only wavelength dependent measurement and when PDL measurement is made over all the wavelength ranges, measurement time becomes too long.
Because of this, in PDL measurement by the polarization scanning method generally, it is constructed so that wavelengths (measurement wavelengths) at which the PDL measurement is made are narrowed to some wavelengths to make measurement by checking wavelength dependence of the measured object.
FIG. 6 is a diagram showing a flow of conventional PDL measurement by a polarization scanning method.
In the case of PDL measurement, wavelength dependent measurement of a measured object is first made (S31). The wavelength dependent measurement is made by measuring transmitted light from the measured object by a power meter while changing a wavelength of light incident on the measured object. When a wavelength is taken as the axis of abscissa and a level (dB) is taken as the axis of ordinate and measured values are plotted, wavelength dependence as shown in FIG. 7 is observed.
Next, a wavelength dependent measurement result is analyzed (S32), and a wavelength at which the PDL measurement is made, namely a wavelength at which loss (or gain) of the transmitted light becomes maximum is read (S33).
Then, measurement wavelengths are set to a measuring device (S34), and PDL measurement is made (S35). The PDL measurement is made by randomly changing a polarization state by a polarization controller every the measurement wavelength.
After the completion of the measurement described above, a wavelength dependent analysis result is associated with a PDL measurement result (S36). That is, processing for arranging the PDL measurement result as a measurement result every the measurement wavelength is performed.
However, in the conventional PDL measurement by the conventional polarization scanning method shown in FIG. 6, an operator performed analysis (S32) of the wavelength dependent measurement result (FIG. 7), reading of the wavelength at which the PDL measurement is made (S33), setting to the measuring device (S34) and association of the wavelength dependent analysis result with the PDL measurement result, so that there were problems that it takes time and effort to make the PDL measurement and also it takes effort to be constructed so that the PDL measurement result can be grasped as a measurement result every the measurement wavelength.
That is, the operator had to hold a value of the read wavelength once in some manner, for example, by making a note even in the case of using an analysis function which the measuring device has with respect to the wavelength dependent analysis.
Also, it is necessary to input the held value to the device one by one to make measurement, so that it took effort to make the measurement. Rather than one or two values to be inputted, inputting several tens of kinds of values one by one to make the measurement is work with enormous effort.
Also, the PDL measurement result obtained finally is not associated with the wavelength dependent measurement result and is acquired individually, so that the operator has to perform the association after the completion of all the measurements.
The invention is implemented in view of such problems of the conventional technique, and an object of the invention is to provide a polarization dependent loss measuring apparatus capable of automatically making PDL measurement and association of a PDL measurement result with a wavelength dependent measurement result.
In order to solve the object, a polarization dependent loss measuring apparatus according to the invention is characterized by comprising wavelength dependent measurement member for measuring transmitted light from a measured object while changing a wavelength of light incident on the measured object, peak wavelength detection member for detecting a wavelength at the time when a level of loss or gain of the transmitted light becomes maximum based on a measurement result by the wavelength dependent measurement member, polarization dependent loss measurement member for measuring polarization dependent loss of the measured object by measuring the transmitted light from the measured object while launching light of a wavelength detected by the peak wavelength detection member into the measured object and also randomly changing a polarization state of the light, measurement result processing member for performing association processing of a measurement result by the polarization dependent loss measurement member with a detection result by the peak wavelength detection member, and output member for outputting a processing result by the measurement result processing member as described in aspect 1.
As a result of this, PDL measurement and association of a PDL measurement result with a wavelength dependent measurement result can be made automatically, so that the PDL measurement can be made easily in a short time and the PDL measurement result can be grasped easily as a measurement result every each the measurement wavelength.
Further, a polarization dependent loss measuring apparatus according to the invention is characterized in that the peak wavelength detection member executes a step of detecting the maximum value of the level from all the wavelength ranges based on the measurement result by the wavelength dependent measurement member, a step of performing a cutback in a measurement level value using the maximum value and a preset threshold value, a step of detecting inflection points of the level in the longer wavelength side and the shorter wavelength side than a wavelength showing the maximum value, and a step of detecting a wavelength corresponding to the maximum value as a wavelength at the time when the level becomes maximum when the inflection points of the level are present in both of the longer wavelength side and the shorter wavelength side than the wavelength showing the maximum value as described in aspect 2.
As a result of this, peak wavelength detection can be performed more surely in the peak wavelength detection member for detecting a wavelength at the time when a level of loss or gain of the transmitted light becomes maximum based on a measurement result by the wavelength dependent measurement member.
Also, a polarization dependent loss measuring apparatus according to the invention is characterized by comprising wavelength dependent measurement member for measuring transmitted light from a measured object while changing a wavelength of light incident on the measured object, notch wavelength detection member for detecting a wavelength at the time when a level of loss or gain of the transmitted light becomes minimum based on a measurement result by the wavelength dependent measurement member, polarization dependent loss measurement member for measuring polarization dependent loss of the measured object by measuring the transmitted light from the measured object while launching light of a wavelength detected by the notch wavelength detection member into the measured object and also randomly changing a polarization state of the light, measurement result processing member for performing association processing of a measurement result by the polarization dependent loss measurement member with a detection result by the notch wavelength detection member, and output member for outputting a processing result by the measurement result processing member as described in aspect 3.
As a result of this, PDL measurement and association of a PDL measurement result with a wavelength dependent measurement result can be made automatically, so that the PDL measurement can be made easily in a short time and the PDL measurement result can be grasped easily as a measurement result every each the measurement wavelength.
Also, a polarization dependent loss measuring apparatus according to the invention is characterized in that the notch wavelength detection member executes a step of detecting the minimum value of the level from all the wavelength ranges based on the measurement result by the wavelength dependent measurement member, a step of performing a cutback in a measurement level value using the minimum value and a preset threshold value, a step of detecting inflection points of the level in the longer wavelength side and the shorter wavelength side than a wavelength showing the minimum value, and a step of detecting a wavelength corresponding to the minimum value as a wavelength at the time when the level becomes minimum when the inflection points of the level are present in both of the longer wavelength side and the shorter wavelength side than the wavelength showing the minimum value as described in aspect 4.
As a result of this, notch wavelength detection can be performed more surely in the notch wavelength detection member for detecting a wavelength at the time when a level of loss or gain of the transmitted light becomes minimum based on a measurement result by the wavelength dependent measurement member.
Further, a polarization dependent loss measuring apparatus according to the invention is characterized in that the output member produces an output by displaying or printing a processing result by the measurement result processing member as described in aspect 5.
As a result of this, an operator can check the processing result outputted by displaying or printing.